Typical safety shut-off systems on drill rigs use a button type switch that is mounted on the control panel and on the opposite side of the drill rig. The switches are connected in series and when one is depressed, the circuit to the ignition of a gasoline engine is broken, causing the engine to stop. With a diesel engine, depressing the switch causes the fuel to be cut off to the engine. Shut-off systems using a button type switch are reliable and effective. However, if someone is caught in rotating drilling tools such as augers, he may not be able to depress the shut-off switches. Another type of shut-off mechanism is described in U.S. Pat. No. 3,515,824. With this type of system a wire is provided that goes through a metal ring. If the wire is moved sufficiently, it will ground out on the metal ring causing the engine to shut off. This type of system is usually placed on the right and left sides of the drill with respect to the rig, generally at the rear of a truck platform on which the rig is mounted, and as in the case of the button type switch, an operator that is caught in the rotating tools may not be able to actuate the shut off wire. The wire-line type system also has the disadvantage of being accidentally activated by loose tools around the rig, hoisting cables, etc. This type of shut-off system requires frequent attention and maintenance. For example, if the tension in the cable is not adjusted properly, it can vibrate, hitting the metal ring and causing accidental shut off. Also the ring and bare cable are exposed and can become corroded and not conduct electricity.
With a mechanically-driven drill, the activation of the shut-off device stops the engine. Because of the inertial forces of the engine flywheel and drive train components, shut off is not immediate. The drive train can make several revolutions.
One of the objects of this invention is to provide a shut-off system that is more readily accessible and more easily actuated than button-type systems in use heretofore, and more easily actuated and at the same time less liable to accidental actuation or disablement than line type systems.
Another object is to provide such a system in which the rotation of the drill is stopped quickly and positively.
Other objects will become apparent to those skilled in the art in light of the following description and accompanying drawings.